The group said to have been targeted has been described as a “terror cell with international ramifications.”

Four of the eight men held - all Moroccan - belong to ISIS and have links to those behind the Brussels bombings last year that killed 32, Mossos d’Esquadra police chief Josep Lluis Trapero said.

Sources close to the investigation told El Periodico that several of those held in raids in and near Barcelona were in the Belgian capital two days before the terror attacks at Brussels Airport and Maalbeek tube station.

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Inside the flat following the police raid

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Spanish police arrested four men over their alleged links to suspects arrested in Belgium over their alleged involvement in the Brussels airport and metro attacks last year

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General view of a flat following a raid by members of the Catalan Regional Police

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Three weapons and £30,000 cash are believed to have been seized during the operation

The men detained are aged between 31 and 39 and have lived in Catalonia for some time, although they are understood to have moved around Europe.

Three weapons and £30,000 cash are believed to have been seized during the operation against radical Islamic terrorism and drug trafficking.

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Mr Trapero described the anti-terror operation as “clearly the most important of its kind carried out so far” by the Mossos d’Esquadra in Catalonia.

He added: “The charges these men are facing could change depending on the material that’s seized in the searches.”

EPA

Police described the raids as "the most important of its kind carried out so far"

A spokesman for the Mossos d’Esquadra said: “This morning officers are carrying out an operation against radical Islamic terrorism and have carried out a dozen raids and searches in Barcelona and surrounding towns.

“The operation represents the final phase of an investigation that began eight months ago.”

The spokesman added: “Investigators detected the existence of a group of criminals linked to Islamic terrorism who were also involved in organised crime.

“The Mossos d’Esquadra informed the Audiencia Nacional who set up a joint investigations team with Belgian authorities.”

Authorities have said they have so far found no evidence the suspects were planning terrorist attacks in Barcelona.

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